In recent years, high density optical discs typified by DVDs (Digital Versatile Discs) have been progressively developed and standardized. To absorb as many different physical record formats of various types of mediums as possible and provide a logical structure of an information storage unit that has a higher commonality in applications, UDF (Universal Disk Format) was established. A rewritable DVD-RAM (DVD-Random Access Memory) uses a logical format corresponding to the UDF. In addition, the UDF can be applied to a one-time writable CD-R and a rewritable CD-RW.
The UDF is structured with a hierarchical file system. In the UDF, with information stored under a root directory, a sub directory and an entity file are referenced. In addition, with information stored in a sub directory, another sub directory and an entity file are referenced. Hereinafter, a directory is abbreviated as “Dir.”.
In other words, a record area on a disc is accessed as sectors. A sector is the minimum unit of storage. On a DVD-RAM, the disc is accessed from the inner periphery side to the outer periphery side. From the innermost periphery side, a lead-in area is formed. The lead-in area is followed by a system area. In the system area, volume information is written. As the volume information, VRS (Volume Recognition Sequence), MVDS (Main Volume Descriptor Sequence), LVIS (Logical Volume Integrity Sequence), and AVDP (Anchor Volume Descriptor Pointer) are written.
The location of a record area at which a file entry (hereinafter abbreviated as “FE”) of the root Dir. is recognized by successively referencing the AVDP, the MVDS, and the FSD. An FE is composed of attribute information for a file or a directory and an allocation descriptor (hereinafter abbreviated as “AD”). An AD is information of a logical address of a file or a directory and a size (length). An AD represents a record area at which entity data of a file is recorded or a record area at which an entity of a directory is recorded.
At the FE of the root Dir., the AD represents a logical address and a length of an entity of the root Dir. The root Dir. contains at least one file identifier descriptor (hereinafter abbreviated as “FID”). With an FID, an FE of a sub directory or an FE of a file under the root directory is referenced. With these FEs, the entity of the corresponding sub Dir. and the entity of the file are referenced by respective ADs. In addition, an entity of a sub Dir. may contain at least one FID. In other words, in the UDF, except for the root Dir., with FIDs and FEs as pointers, the FIDs, FEs, and entities are successively accessed and recognized. In the UDF, FIDs, FEs, and entities can be written any recordable areas.
For example, on the innermost periphery of a disc, the lead-in area is formed. On the outer periphery of the lead-in area, a system area is formed. The entity of the root Dir. is formed for example on the outer periphery of the system area.
Next, the case that a file is accessed from the root Dir. through a sub Dir. will be described. Corresponding to the FID of the entity of the root Dir., an FE of the sub Dir., the FE being at an address physically apart from the entity of the root Dir., is referenced. Likewise, corresponding to an AD of an FE of the sub Dir., the entity of the sub Dir., the entity being at an address apart from the FE of the sub Dir., is referenced. Likewise, the FID of the entity of the sub Dir. is referenced. An FE of the file, the FE being at an address apart from the entity of the sub Dir., is referenced. With an AD of the FE of the file, the entity of the file, the entity being at an address apart from the FE of the file, is referenced.
Thus, conventionally, when information of directories and files is dispersed on a disc, it takes a long time to read these information. To solve such a problem, it is possible to collectively record pointer information such as FIDs and FEs at a predetermined area of a disc.
However, in such a case, if a file is deleted from a disc, since a corresponding FE and so forth are deleted, blank addresses take place. In this case, a file may be written to a blank address. As a result, pointer information that has been collectively written to the predetermined area may be separated. As a result, it may take a long time to read information of directories and files.
In addition, while the disc is being used, if any defect takes place in hierarchical structure management information for a file system, the management information being composed of pointer information such as FIDs and FEs, the drive apparatus cannot read the management information. In addition, while the disc is being used, if any defect takes place in an FE of a file, the FE representing a record area (location) of entity data of the file, the drive apparatus cannot read the FE of the file. In such a case, even if any defect does not take place in entity data of moving picture data or audio data, since the drive apparatus cannot read the management information or the FE of the file, the drive apparatus cannot access the entity data.